1. Field of the Invention
The present invention relates to an apparatus for fabricating multi-layer spiral tubes in which the multi-layer spiral tube is formed by spirally wrapping a web in a plurality of layers, and especially to such an apparatus which can be favorably utilized for fabrication of a cylinder section of a high-pressure pressurized container, a large-diameter steel tube for high-pressure piping, or the like.
2. Description of the Prior Art
Heretofore, upon fabrication of thick-walled large-diameter tubular materials, an apparatus for fabricating tubes according to a spiral wrapping system has been employed. Since this apparatus forms a multi-layer spiral tube by wrapping a web around an inner tube which serves as an inner lining, it can fabricate a thick-walled large-diameter tube having an arbitrary diameter without being restricted by the width of the web, and moreover, it can easily achieve even multi-layer wrapping, so that after it is used generally to fabricate a large-diameter cylinder for high-pressure use such as a cylinder for a high-pressure pressurized container or a large-diameter steel tube for high-pressure piping.
With regard to the above-referred apparatus for fabricating tubes according to a spiral wrapping system, reference could be made to the disclosure in, for instance, Japanese Laid-Open Utility Model Specification No. 57-52237.
In such type of apparatus in the prior art, due to the fact that the respective means for performing rotation of an inner cylinder and movement in the longitudinal direction thereof upon spirally wrapping a web, feeding and wrapping of the web, welding of adjacent edge portions of the web, and grinding of excess metal of welding were not adapted to operate in correlation with one another, operators had to be posted at the respective means and variations of operating conditions had to be responded according to individual judgement of every operator. In addition, due to the fact that the operations of wrapping the web, welding the edge portions of the web, grinding excess metal of welding and non-destructively inspecting the welded portions has to be carried out separately, a lot of labor was necessitated. Furthermore, upon wrapping the web around the inner cylinder, for the purpose of bringing the web into tight contact with the inner cylinder and minimizing the gap clearance between the layers it was necessary to urge the web against the inner cylinder by means of depressing rolls, but it was extremely difficult to apply a proper urging force because the urging forces of the respective rolls had to be manually adjusted. Consequently, often degradation of quality of the products was resulted due to partial increase of the gap clearance between the layers, non-uniformity of the gap between the adjacent edge portions of the web, or generation of a gap clearance between the layers in the peripheral portions of the weld caused by welding strain. Accordingly, the known fabricating apparatus in the prior art had a shortcoming that it cannot fabricate multilayer spiral tubes of high quality and low cost.